Organic polysulfides are useful for many purposes such as additives for elastomers, antioxidants for lubricating oils, intermediates for the production of organic chemicals, insecticides, germicides and as an additive to diesel fuels to improve the cetane number and ignition qualities of these fuels. These compounds are also useful in the compounding of extreme pressure lubricants and in the acceleration of rubber treating processes.
Such polysulfide compounds can be prepared by reacting mercaptans with elemental sulfur in the presence of a basic catalyst. For example, Biesan et al (U.S. Pat. No. 3,308,166) discloses that polysulfides can be prepared from a mercaptan and sulfur catalyzed by an amine using an alcohol promoter.
A conventional process for producing a polysulfide compound such as di-t-dodecyl polysulfide is to react a mercaptan such as t-dodecyl mercaptan with elemental sulfur in the presence of triethylamine as catalyst. However, the polysulfide thus prepared is associated with as high as 19 weight % of unreacted mercaptans and residual H.sub.2 S contributing to unpleasant odor and an unsatisfactory product. Additionally, high content of unreacted mercaptans indicates an incompletion of the reaction towards polysulfide. Further, possibly because of the unreacted mercaptans and the amine catalyst, the product always becomes very unstable, i.e. the product turns cloudy, probably due to degradation of the polysulfide causing precipitation of sulfur. These problems greatly reduce the desirability and utility of the polysulfide product.
Kamii et al (Japanese Applicant 58-140,063) discloses a process for deodorizing dialkyl polysulfides by contacting the polysulfide-bearing fluid with 1,2-epoxy compounds. The 1,2-epoxy compound apparently react directly with the unreacted mercaptan and hydrogen sulfide, thereby producing a product with reduced odor. Excess 1,2-epoxy compounds are reportedly removed by convention methods, such as vacuum distillation.
However, due to the high content of unreacted mercaptans, as described above, such treatment greatly reduces the yield of an organic polysulfide compound. Additionally, employing the process disclosed in Kamii et al produces a product that still has such high mercaptan level that it would contribute the instability of a polysulfide product. It would therefore be a significant contribution to the art to develop a catalyst and a process using the catalyst for producing a polysulfide product having substantially reduced unreacted mercaptans so that the product is stable and is made more useful for industrial uses.